In today's wireless radio systems, different mobile radio standards such as Global System for Mobile Communication (GSM), Enhanced Data Rates For GSM Evolution (EDGE), and Universal Mobile Telecommunications Standard (UMTS) are used. Data transmission in these and other systems is performed using radio frequency signals.
Before sending the radio frequency signals, for example over an antenna in a mobile radio device, the radio frequency signals are usually amplified by a power amplifier. The transmitting power or output power of the power amplifier can depend on a position of the mobile radio device. For example, a higher transmitting power is needed if the mobile radio device is at a further distance from a base station. A higher transmitting power can also be needed if the mobile radio device is transmitting a radio frequency signal comprising data at a higher data rate.
It can be necessary to be able to switch between different values of transmitting power with short switching times to achieve a sufficient power consumption and a good transmitting quality. In many cases, the transmitting power can be adjusted by providing a controlled working current to the power amplifier which, for example, is provided by a digital/analog converter (DAC) with a current output.
The DAC can be a voltage DAC providing an output voltage corresponding to a control word, wherein the output voltage is converted to a current by a voltage-to-current converter. The voltage DAC usually comprises a plurality of converting stages which degrade an accuracy and a noise performance of the DAC.
The DAC can also be realized as a current DAC comprising a plurality of binary weighted current sources, which are controlled by a binary control word, or a plurality of equally weighted current sources which are controlled by a thermometer coded control word. In case of the binary weighted current sources, it can happen that the output current is not monotonic in view of the binary control word; that means an output current can be decreased for an increasing binary control word. In case of the equally weighted current sources, a control logic for generating the thermometer coded control word from a respective binary control word can be space consuming for a higher word length of the control word when realized in an integrated circuit.